Exotic Stars: Extreme Physics Flashcards
How do exotic stars form?
Nuclear fuel runs out
Thermal pressure fails
Gravitational collapse to smaller size
New equilibrium between gravity and quantum degeneracy pressure
What kind of stars are exotic?
White dwarf stars
Neutron stars
Why are exotic stars useful?
Strong tests of quantum mechanics, special and general relativity
Type 1a supernova
When a white dwarf has a companion and explodes
How much energy is released in a type 1a supernova
Suns lifelong output
How hot is a type 1a supernova
100 Tsun
How bright is a type 1a supernova
5 billion x Lsun (about a galaxy)
Mysteries of the type 1a supernova
Single/double degenerate progenitors
How does the explosion happen in detail
Type 1a supernovae - recent supercomputer simulations
Ignition not from gravitational collapse?
Pressure and temp slowly increase until Tcore reaches fusion temp right before M reaches Mch
Small flame bubble starts near centre
OR
Nuclear burn (flame starts from carbon fusion,oxygen fusion stars later, subsonic deflagration -> supersonic detonation)
Type II supernova
Stars mass > 8-10 sun
Onion layered fusion with Inert nickel iron core (WD) supported by electron degeneracy pressure
Nickel iron ash deposited until core mass reaches Mch and collapses
Electrons squish until they fuse with protons to make neutrons
Outer shell free falls in
Type II supernova what is the collapse halted by? What happens after?
Repulsive strong force and neutron degeneracy
There’s a bounce
Them an outward moving shockwaves
Only sun’s lifetime output involved in visible blast which leaves behind rest
Mysteries of Type II supernova
Nature of short range nuclear forces
How burst of neutrinos converts 1% of energy to produce shock wave that causes SN explosion
Hypernovae, gamma ray bursts etc
What are neutron stars?
Giant atomic nucleus
Strong gravitational field
Strong magnetic field
Rapid rotation - pulsar
How do you get from white dwarf to neutron star
me -> mn ~ mp
Mu=2 -> mu=1
Chandrasekhar limit
1) Emax = cp
2) p max = cNe^1/3h/2R
3) Pmax = NkT/V = N/V (2Emax/3)
4) Pc = Pmax
Inert white dwarf
Core held up by electron degeneracy pressure
H burning she’ll deposits ash, growing core
Wind from burning expels outer layers - red giant - planetary nebula
Wind is fast enough that M doesn’t exceed Mch
White dwarf supernova
WD core orbiting companion star H pulled onto WD by tidal forces M slowly increases until M=Mch Supernova Nuclei free fall until gravity Temp up Flash nuclear burn
Death of a high mass star
1) more massive core - hotter core
2) loss of mass during giant phase can’t keep mass less than Mch
Parts of a supernova
Collapse
Bounce
Explosion
Supernova - collapse
Core - gas of e and Fe, v->c
Gravitational collapse
Beta decay happens (n formed)
Supernova - bounce
Repulsive nuclear force at short distance
Neutron degeneracy pressure
Supernova - explosion
Energy of stellar mass is only 10^44J
Neutrinos carry away almost all the 10^46J of gravitational PE
Neutron stars
All nuclei have same density
Strong nuclear force has hard core of repulsion (not understood)
Stabilized by gravity (against repulsive force)
Neutron stars - strong gravitational field
Can use Newtonian gravity as rough approx
